Hybrid electric vehicles (HEVs) include a high voltage traction battery for supplying power to an electric motor used to propel the vehicle. The traction battery may include several battery modules, each having an array of individual battery cells capable of delivering and storing electric energy to and from the electric motor. Use of the fraction battery during travel may cause the temperature of individual battery cells within the battery modules to increase. Air-cooled and fluid-cooled systems have been developed to introduce relatively cool air or liquid into the traction battery while removing undesirable heat from within. This inhibits the battery from overheating, which would otherwise cause the battery to operate less efficiently.